Quarterly report pursuant to Section 13 or 15(d)

Revenue and Contract Costs - Pass Through Costs (Details)

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Revenue and Contract Costs - Pass Through Costs (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Contractors [Abstract]        
Pass-through costs as a percentage of revenues 48.40% 33.80% 45.30% 35.00%